1. Field of the Invention
The present invention relates to a pneumatic tire provided with a land part (blocks, ribs, and the like) in a side wall region as well and in more detail, the present invention relates to improvement in visibility of marks displayed in a side wall region, prevention of poor tire manufacture, and improvement in tire durability.
2. Description of the Prior Art
In a pneumatic tire, marks such as letters showing manufacturer's names, brand names, tire sizes, and the like, and graphics showing tire rotating directions are sometimes displayed in a side wall region. From the view point of durability, display by coloring and coating has many drawbacks. Therefore, usually, marks are displayed letting them protruded from a side wall surface. Further, like a pneumatic tire disclosed in patent Japanese Patent Laid-Open Publication No. 63-106109, visibility of marks is improved by outlining edge parts of the marks with projection bars called ridges.
By the way, rubber thickness of a tire side wall is relatively thin compared with tread thickness or bead thickness. In order to improve durability of a sidewall or steering stability, means to enhance rubber hardness or means to increase rubber thickness of a side wall have been employed. However, the employment of such means causes the increase in tire weight, and therefore, such means have not been effective.
For this reason, to improve durability or steering stability, for example, a land part is extended from a tread region to a side wall region thereby reinforcing the side wall. In this case, consideration has been made to avoid overlap of a land part and marks. To be specific, position of the marks has been changed, marks themselves have been changed, or size thereof has been reduced. However, since marks are important elements of tire designs, reduction in size of the marks themselves has had a drawback of degradation in merchandize.
Conversely, putting more importance on visibility, visibility of the marks can also be enhanced, allowing the overlap of the land part and the marks and making protruded height of the marks greater than height of the land part. However, this has a drawback of degradation in tire durability or in performance such as increased tire weight, cracking at a base part of the marks, and the like. In addition, when protruded height of the marks increases, poor manufacture at a time of the vulcanizing and molding is likely to occur such as difficulty in molding of the marks (due to rubber shortage). Therefore, with the requirement of adding vent holes or with the requirement of consideration of the cross-sectional shape of the marks, cost of molds has increased.
The object of the present invention is to achieve visibility of marks, prevention of poor manufacture, and improvement in durability of a tire in a pneumatic tire provided with a land part which reinforces a side wall.